Electrochemical plating (ECP) is a copper (or other metal) deposition technique that is being developed and is likely to become the preferred commercial filling process. In this method, a wafer is immersed in a copper electrolytic bath. Since the wafer is electrically biased with respect to the bath, copper electrochemically deposits on the wafer in a generally conformal process. Electroless plating techniques are also available. Electroplating and its related processes are advantageous because the processes can be performed with simple equipment at atmospheric pressure, deposition rates are high, and liquid processing is consistent with subsequent chemical mechanical polishing.
Electroplating, however, imposes several requirements. A copper seed and adhesion layer is required on top of the barrier layer, such as of Ta/TaN, to nucleate the electroplated copper and adhere it to the barrier material. A good conductive seed and adhesion layer must be deposited if the electroplating is to effectively fill the bottom of the via hole.
A copper seed layer deposited over the barrier layer is typically used as the electroplating electrode. However, the layer's integrity must be assured, and a continuous, smooth and uniform film is preferred. Otherwise, the electroplating current will be directed only to the areas covered with copper or may be preferentially directed to areas covered with thicker copper.
Copper electroplating is commonly used for producing low-resistance and reliable interconnections. For damascene processes, the trench and via are first defined and a thin barrier layer of about 300 Å thickness and a copper seed layer of about 2000 Å thickness are arranged on the wafer surface before copper electrochemical plating. Because ECP is performed in a liquid state, the electrolytic solution must completely cover the surface to achieve a uniform copper deposition.
However, since the wafer surface is not smooth, a superfill process is needed and can be achieved through additional additives often comprising polymer chains that degrade the wetting ability between the electrolytic solution and the copper seed layer. A measure of wetting ability is contact angle, i.e., the greater the contact angle, the poorer the wetting ability of the surface, and conversely, the less the contact angle, the better the wetting ability of the surface. Poor wetting ability often leads to defects in the ECP examples of which are shown in FIGS. 1a and 1b. In FIG. 1a an air bubble defect is shown as a result of poor wetting ability of the seed layer. In FIG. 1b a bubble pit defect is shown. These defects are especially probable on aged copper seed layers. An unwanted copper thin film profile is observed which cannot meet standard requirements.
Several prior art methods are directed to ECP. U.S. Pat. No. 6,258,223 issued to Cheung, et al. describes an in-situ electroless copper seed layer enhancement in an electroplating system. U.S. Pat. No. 6,194,307 issued to Chen, et al. describes a method to eliminate copper line damages for damascene processes. U.S. Pat. No. 6,582,569 issued to Chiang, et al. describes a process for sputtering copper in a self-ionized plasma.
Accordingly one or more embodiments of the present subject matter are directed to providing a novel method of improving copper electroplating. The present subject matter presents a structure having a dielectric layer formed thereover with a dielectric layer having an opening formed therein. The opening is lined with a metal seed layer and the metal seed layer is treated with a cleaning process to increase wetting ability and thereby prevent defects in the metal plating. A metal layer is then formed upon the metal seed layer.
These and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description of the preferred embodiments.